1. Field of the Invention
The present invention relates to a tilt-angle detecting apparatus for a motorcycle, and a method of detecting a tilt angle in a motorcycle. More particularly, the present invention relates to a tilt-angle detecting apparatus which obtains a tilt angle of a vehicle body based on a vehicle speed and a steering angle during a turning operation of the motorcycle while driving.
2. Description of the Background Art
There are several known control apparatus for a motorcycle having a controller for controlling an optical axis or the like based on a tilt angle of a vehicle (motorcycle) body determined by a tilt angle detecting apparatus.
An example of such a tilt-angle detecting apparatus for a motorcycle is disclosed in the Japanese Unexamined Patent Application Publication No. Hei 5-208635. The disclosed tilt-angle detecting apparatus is mounted on a motorcycle equipped with relatively wide tires, in which a point of contact between the tire and the ground is shifted in a width direction of a vehicle (motorcycle) body in response to the banking of the vehicle body, i.e., tilting in the width direction of the vehicle body.
This known tilt-angle detecting apparatus, having an acceleration sensor, detects the acceleration in the width direction of the vehicle body. The tilt angle is detected by checking the acceleration thus detected, compliant to a correspondence table of acceleration and tilt angle, which has been prepared in advance.
According to the Japanese Unexamined Patent Application Publication No. Hei 5-208635, the tilt angle is obtained based on unique acceleration in the width direction of the vehicle body. Such method of determining a tilt angle of the motorcycle, however, has its own drawbacks.
For example, while turning the vehicle to the right, when a driver of the motorcycle decides to quickly turn to the left, the acceleration in the width direction of the vehicle body shows a high value even when the motorcycle is at an upright position. This results in an erroneous determination that the motorcycle is tilting (leaning). In particular, the changes of tilt angle in every moment may probably result in a calculation of a tilt angle with lower precision.
Incidentally, it is well known that the tilt angle of a motorcycle is determined as a function of three unknown variables: a steering angle, a vehicle speed, and a turning radius of the motorcycle. Here, in the given example of the Japanese Unexamined Patent Application Publication No. Hei 5-208635 it is difficult to obtain a precise turning radius while the motorcycle is traveling, when while turning the motorcycle to the left, the driver quickly decides to turn the motorcycle to the right. Accordingly, it is desirable to provide a high precision tilt-angle detecting apparatus which employs a simplified method of arithmetic operations for more precisely calculating a tilt of the vehicle, and which is capable of dealing with a wide range of running conditions of the vehicle during operation thereof.
The present invention has been made to overcome such drawbacks. Accordingly, it is one of the objects of the present invention to provide a tilt-angle detecting apparatus for a motorcycle for more precisely calculating a tilt angle of the vehicle body using a simplified method of arithmetic operations.